In known methods for processing screw rotors, a blank for screw cutting is provided in a first shaft and tools are set in a second shaft whose rotational axis is orthogonal to that of the first shaft. These first and second shafts are synchronously rotated by external means. At the beginning of processing grooves, the entire tools are compressed in the second shaft. When the process proceeds, the tools are progressively expanded out into a screw.
This is disclosed in PCT Japanese Translation Patent Publication No. Hei 6-506640 (FIGS. 2, 3, 4, 5, 6, 7, 14 and the like), for example.
In the known processing methods, accuracy of finishing is compromised due to various factors such as groove size and installation position of tools, distance between the rotational axis of the first shaft and that of the second shaft, or accuracy of the processing apparatus. Specifically, in a process using a forming tool, the cutting resistance at the groove bottom is very large and thus micro-cutting, that is, 0.04 mm in one cut at most is required. Furthermore, the entire cut length becomes long, which exerts adverse effects on the improvement in the processing time and service life of the tool.
Furthermore, with the known methods for processing screw rotors, if production of the particular processing apparatus intended for processing the screw rotor is discontinued, the screw rotor cannot be manufactured.
Moreover, since grooves on the screw rotor have complex shapes, a special measuring device is necessary to measure the grooves. Therefore, in the known processing methods, a measuring step is provided as an additional step. Accordingly, a workpiece is detached from the processing apparatus during the process and is measured to determine whether the groove has predetermined dimensions. After the measurement, the workpiece is returned to the process.
To solve the above described problems, it is a first object of the present invention to provide a method and an apparatus for processing a screw rotor in which a groove with a complex shape and the inner and outer surfaces of the screw rotor are efficiently processed with high accuracy using a commercially-available five-axis NC machine tool and to provide a cutting bit for use in the processing apparatus and method.
A second object of the present invention is to provide a method and an apparatus for processing a groove with a cutting depth that enables high processing efficiency, for the purpose of solving the problem of having a small cutting amount in the process using the forming blade due to cutting resistance at the groove bottom.
A third object of the present invention is to provide a method and an apparatus for processing a screw rotor in which the accuracy of the shape of a groove, which is determined depending on the processing apparatus, arrangement, and tool in the known processing method and apparatus, can be readily modified.
A fourth object of the present invention is to provide a method and an apparatus for processing a screw rotor in which the accuracy of the shape of a groove processed by the apparatus can be measured and modified, which is not possible with known processing apparatuses.
A fifth object of the present invention is to provide a method and an apparatus for processing a screw rotor in which both an inexpensive commercially-available tool and an expensive special tool are used in combination to process the screw rotor so that the expensive special tool can have a long service life and the overall expenses of the tools can be reduced.
A sixth object of the present invention is to provide a method and an apparatus for processing a screw rotor in which the screw rotor is processed without a shaft, which is provided in the screw rotor in the known methods, and thus costs of processing and facilities are reduced.